Characteristics of Drought-flood Abrupt Events During Growing Season in the Songhua River Basin

Drought-flood abrupt event refers to the extreme climatic event in which a region rapidly transitions from a drought to a flood state (or vice versa) within a relatively short period. As a typical compound event, its impact is far greater than that of droughts or floods occurring independently. Such events can significantly impact agricultural production, water resource management, ecological environments, and socio-economic conditions. Characteristics of drought-flood abrupt during crop growing season in the Songhua River Basin from 1950 to 2023 are investigated, and spatiotemporal changes in the risk index of these transitions are also analyzed, providing a scientific basis for climate change research, water resource planning, and enhancing the ability to cope with extreme climate events. It's found that the frequency and impact range of drought-to-flood transitions during the growth season in the Songhua River Basin are generally higher than those of flood-to-drought transitions, with the intensity of both being roughly equivalent. May and June are high incidence periods for abrupt droughts and floods. Since 1990, the frequency, intensity, and variability of the drought-flood risk index have been significant. The frequency of transitions from drought to flood is relatively high in Heihe, Nenjiang, and southeastern part of Jilin. In contrast, the intensity of these events is greater in the eastern part of the Songnen Plain and the Daxing'anling region. From 1950 to 2023, the risk index of drought-to-flood transitions in the Basin has shown an increasing trend; contributions of the risk index for drought-to-flood transitions in May and June are relatively large, especially in the northern and northeastern part in May and the central region in June; the contribution in July is relatively small. The frequency of transitions from flood to drought is relatively high in the Sanjiang Plain and the southeastern part of Jilin, with greater intensity observed in the central area of the Songnen Plain. From 1950 to 2023, the risk index for transitions from flood to drought has increased; however, this trend is not statistically significant. In the past 20 years, the interannual variability of the frequency and risk index of drought-to-flood transitions has been significant, and they are also significant around 1970 and from 1995 to 2010. The risk index contribution of flood-to-drought transitions in July across the Basin is substantial, with notable contributions in May for the northern and western parts, and in June, July, and September for the eastern part. Changes in precipitation variability may directly influence the abrupt risk index of drought and flood in the Songhua River Basin.